1. Field of the Invention
The present invention relates to a reproducing head and a magnetic disk drive using the reproducing head.
2. Description of the Related Art
In association with a reduction in size and an increase in recording density of a magnetic disk drive in recent years, the flying height of a head slider has become smaller and it has been desired to realize contact recording/reproduction such that the head slider flies a very small height above a recording medium or comes into contact with the recording medium. Further, a conventional magnetic induction head has a disadvantage such that its reproduction output decreases with a decrease in peripheral speed of a magnetic disk as the recording medium (relative speed between the head and the medium) caused by a reduction in diameter of the magnetic disk. To cope with this disadvantage, there has recently extensively been developed a magnetoresistive head (MR head) whose reproduction output does not depend on the peripheral speed and capable of obtaining a large output even at a low peripheral speed. Such a magnetoresistive head is now a dominating magnetic head. Further, a magnetic head utilizing a giant magnetoresistive (GMR) effect is also commercially available at present.
With higher-density recording in a magnetic disk drive, a recording area of one bit decreases and a magnetic field generated from the medium accordingly becomes smaller. The recording density of a magnetic disk drive currently on the market is about 40 Gbit/in2, and it is rising at an annual rate of about 200%. It is therefore desired to develop a reproducing head which can support a minute magnetic field range and can sense a change in small external magnetic field.
At present, a spin valve magnetoresistive sensor utilizing a spin valve GMR effect is widely used in a magnetic head. The spin valve magnetoresistive sensor has a spin valve magnetoresistive film as a multilayer film including a free ferromagnetic layer (free layer) in which the direction of magnetization changes according to an external magnetic field, a nonmagnetic conductive layer formed adjacent to the free layer, a pinned ferromagnetic layer (pinned layer) formed adjacent to the nonmagnetic conductive layer, and an antiferromagnetic layer formed adjacent to the pinned layer for fixing the direction of magnetization in the pinned layer. The antiferromagnetic layer is formed of an antiferromagnetic material.
In the spin valve magnetoresistive film, a relative angle of the direction of magnetization in the free layer to the direction of magnetization in the pinned layer changes to produce a change in resistance. In the case that the direction of magnetization in the free layer is the same as the direction of magnetization in the pinned layer, the resistance becomes a minimum value, whereas in the case that the direction of magnetization in the free layer is opposite to the direction of magnetization in the pinned layer, the resistance becomes a maximum value. In the case of using this magnetoresistive sensor in a magnetic head, the magnetization direction in the pinned layer is fixed to a direction along the height of a magnetoresistive element, and the magnetization direction in the free layer in the condition where no external magnetic field is applied is generally designed to a direction along the width of the magnetoresistive element, which direction is perpendicular to the pinned layer. Accordingly, the resistance of the spin valve magnetoresistive film can be linearly increased or decreased according to whether the direction of the signal magnetic field from the magnetic recording medium is parallel or antiparallel to the magnetization direction of the pinned layer. Such a linear resistance change facilitates signal processing in the magnetic disk drive.
In the magnetoresistive head, a pair of electrode terminals are provided in relation to the magnetoresistive film, and a sense current as a constant current is passed from the pair of electrode terminals through the magnetoresistive film during operation of the magnetoresistive head. When the spin valve magnetoresistive head is relatively moved in proximity to a magnetic disk in the condition where the sense current is passed through the magnetoresistive film, the electrical resistance of the magnetoresistive film changes according to a signal magnetic field from the magnetic disk, and a reproduction signal having an output voltage represented as the product of this electrical resistance and the amperage of this sense current is output.
With an increase in recording density of a magnetic disk drive, the core width (sense region) of a read element formed between a pair of electrodes becomes smaller, and a manufacturing process for attaining such a smaller core width to be required becomes remarkably difficult. Accordingly, there are many problems including low yield and high cost.